This blog post does a pretty good job of answering this question. I'll pick out a couple of the most relevant points.
First, the report itself should be taken with a grain of salt. It appeared on RT.com (which has a history of publishing stories with inflammatory headlines), and cites a story from a Russian news paper which quotes an unnamed source as saying the ban is "under consideration". Hardly convincing.
Second, the inventory of existing engines is enough to keep the Atlas program going for "several years", according to ULA.
Finally, if necessary, production of the engines could (theoretically) be done in the U.S. The article notes that this was one of the conditions of allowing the use of a Russian engine in the EELV program. The article also notes, however, that there have long been doubts about whether Russia would actually hand over the blueprints.